EP0166726A1

EP0166726A1 - 10-ethyl-8,10-dideazaminopterins.

Info

Publication number: EP0166726A1
Application number: EP84900591A
Authority: EP
Inventors: Joseph I Degraw; Lawrence F Kelly; Francis M Sirotnak
Original assignee: SRI International Inc; Stanford Research Institute
Current assignee: SRI International Inc
Priority date: 1983-12-27
Filing date: 1983-12-27
Publication date: 1986-01-08
Also published as: AU2435784A; GB2160525B; DE3390563C2; GB8518606D0; WO1985002844A1; EP0166726B1; DE3390563T1; AU559561B2; GB2160525A; JPS61500845A

Abstract

8,10-didéazaminoptérines de formule (I) où R représente un méthyle ou un éthyle, leur carboxylate et leurs sels d'addition acide. Ces composés présentent une activité antinéoplastique similaire à celle du méthotrexate ou à d'autres analogues didéaza, mais plus efficace.8,10-dideazaminopterins of formula (I) in which R represents methyl or ethyl, their carboxylate and their acid addition salts. These compounds have an antineoplastic activity similar to that of methotrexate or other dideaza analogs, but more effective.

Description

8,10-DIDEAZAMINOPTERINS

Description

Reference to Government Grant

The invention described herein was made in the course of work under grants from the National Institute of Health.

Technical Field

The invention is in the field of pterin chemistry and cancer therapy. More specifically it concerns 8, 10-dideazaminopterin and its 10-alkyl analogs and their use as antineopiastic agents.

Background Art

Aminopterin and its N-10-methyl derivative, methotrexate, have long been recognized as powerful antineopiastic agents. Methotrexate has enjoyed some thirty years of acceptance as a clinically useful anti-cancer drug. The drugs are antimetabolites inhibiting dihydrofolate reductase (DHFR). They affect both neoplastic and normal host tissue. J.I. DeGraw and F.M. Sirotnak, Cancer

Treatment Reports, 62, 1047 (1978), British Patent 1,534,238, dated November 29, 1978 and U.S. application serial no 75,913, filed 17 September 1979 report that 10-deazaminopterin exhibited more potent antitumor activity than aminopterin and methotrexate in experimental tumors in mice. Specifically, it was found to have a wider spectrum of activity, better penetration of tumor tissue and more favorable distribution and kinetic parameters for tumor versus normal tissue. The cited U.S. patent application also teaches that antitumor effect and the spectrum of activity of 10-deazaminopterin were enhanced by incorporation of alkyl groups of short chain length at the 10 carbon atom. Alterations of the pteridine ring of folic acid have also been investigated. The synthesis and antifolate activity of 8-deazafolic acid was reported by J.I. DeGraw, R.L. Kisliuk, Y. Gaumont and CM. Baugh J Med Che, (1974) 1/7:470 and 8,10-dideasafolic acid was reported in J.I. Degraw, R.L. Kisliuk, V.H. Brown and Y. Gaumont, Chem Biol Pteridines (1979) 6:229. Both of these compounds were active anti-folates, but did not significantly affect DHFR. A. Srinivasan and A.D. Broom, J Org Chem (1981) 46;1777 reported the preparation of 8-deazaminopterin and 8-deazamethotrexate, but did not report biological activity for the compounds.

More recently, it was disclosed that 8,10-dideazaminopterin exhibited bioloigcal activity (DeGraw, J.I., et al, J Hetero Chem, (1982) 19:1587. A poster session at the International Symposium on Pteridine and Folic Acid Analogs, Scotland in September 1982 disclosed prepraration of the n-propyl analog. It has now been found that 10-methyl-8,10-dideazaminopterin and 10-ethyl-8,10-didiazaminopterin have surprisingly potent anti-neoplastic activity as compared with the unsubstituted and n-propyl analogs.

Disclosure of the Invention

The compounds of the invention are 8,10-dideazaminopterins of the formula:

where R is methyl or ethyl and pharmaceutically acceptable salts thereof. These compounds have exceptional anti-neoplastic activity. Antineopiastic compositions containing the compounds comprise a therapeutically effective amount of one or more of the compounds in combination with a pharmaceutically acceptable carrier. Living animals, including humans, are treated for cancer by administering therapeutically effective amounts of such compositions, typically in a unit parenteral dosage form, to the animal.

Modes for Carrying Out the Invention

The pharmaceutically acceptable salts of these compounds include acid addition salts and carboxylate salts. These salts are "pharmaceutically acceptable" in that they are nontoxic and functionally equivalent to the base compound(s). Acid addition salts are formed by reacting one or more of the free NH₂ groups of the methyl or ethyl 8, 10-dideazaminopterins with an appropriate acid. Suitable acids include inorganic acids, for example, hydrochloric, hydrobromic, nitric, sulfuric or phosphoric acid; organic carboxylic acids such as glycoliσ, hydroxy maleic, malic, tartaric, citric, salicylic, o-acetyloxybenzoic, nicotinic and isonicotinic acid; and organic sulphonic acids such as methanesulfonic, ethanesulfonic, 2-hydroxyethane sulfonic, p-toluenesulfonic or naphthalene-2-sulfonic acid.

Carboxylate salts are formed by reacting a suitable base with one or more of the free carboxylic groups of the methyl or ethyl 8,10-dideazaminopterins. Suitable bases include alkali metal or alkaline earth metal hydroxide, potassium hydroxide, calcium hydroxide, magnesium hydroxide and corresponding carbonates; and nitrogen bases such as ammonia and alkylamines such as trimethylamine, and triethylamine.

The compounds of this invention may be synthesized by the following route:

The reaction scheme as shown uses the synthesis of the 10-ethyl derivative and is. illustrative.

In step 1, the alkyl iodide (2) is reacted with a homoterephthalate ester (1). Any common homoterephthalate ester may be used, and the intermediate anion in the alkylation is generated by suitable base, such as alkali hydride, hydroxide or alkoxide in a polar aprotic solvent such as DMF or THF. The reaction is quenched with acid, and the intermediate α-alkyl homoterephthalate isolated.

In step 2 the bromomethyl compound (4) is used to alkylate the anion of the dimethyl α-alkyl homoterephthalate. Any common ester of the acid portion of (3) may be used and the anion may be generated by alkali hydrides, alkoxides, hydroxides and other bases obvious to one skilled in the art. A suitable polar aprotic solvent such as dimethyl formamide is employed. The 10-carboxylate compound (5) so obtained is treated in dimethyl sulfoxide or hexamethyl phosphoramide solvent with an alkali metal halide or cyanide to cause cleavage of the 10-carboxylate ester with subsequent decarboxylation of the 10-carboxylic acid to afford a 2,4-diaminopteroic acid intermediate (6). The useful temperature range for the process is 100º-200ºC, preferably about 170º- 180°C. The pteroic acid compound (6) is then coupled with diethyl L-glutamate (7). Activation of the carboxylate moiety of (6) is achieved via the mixed anhydride as generated in the presence of isobutyl chloroformate and triethyl amine. Other chloroformate esters along with other organic bases would be suitable for this purpose. The pteroyl glutamate diester (8) so obtained is hydrolyzed via treatment with an alkali hydroxide or carbonate in aqueous alcoholic medium, preferably aqueous 2-methoxy-ethanol to give the 10-alkyl-8,10-dideazaminopterin (9).

Mode of Administration

The physiological properties of 8,10-dideazaminopterins of the invention are similar to methotrexate. Accordingly they may be formulated for use as antineopiastic agents in a manner similar to methotrexate. Such formulations will comprise the 8,10-dideazaminopterins dissolved/suspended in pharmaceutically acceptable liquid carrier such as mineral oil or saline or mixed with pharmaceutically acceptable solid carriers such as talc, magnesium stereate, starches, and sugar, and if desired, formed into dosage forms such as tablets, cachets, suppositories and capsules. As used to describe such carriers the term "pharmaceutically acceptable" means that the carrier is nontoxic, generally inert, and does not affect the functionality of the active ingedient(s) adversely. The term carrier includes materials that are sometimes referred to as diluents or vehicles in the pharmaceutical formulation art. The 8,10-dideazaminopterins will mainly be used as aqueous solutions of their sodium salts for administration intraveneously or subσutaneously. The dose and the dosage regimen will depend upon the neoplasm being treated, the mode of administration, the animal species involved, and the weight of the subject. The dosage will typically range between about 0.1 to 500 mg/day. Treatment will typically be given daily until the neoplasm is in remission. Maintenance treatments during remission will typically be made on an intermittent basis.

The compounds may be administered parenterally (e.g. intravenous, intraarterial, intraperitoneal, intramuscular, intrathecally, subcutaneously) or orally. They are effective in treating leukemias, lymphomas, and solid tumors such as choriocarcinoma, hydatidiform mole, chorioadenoma destruens, acute lymphocytic leukemia, mycosis fungoides, esteogenic sarcoma, lymphosarcoma, and other non-Hodgkin's lymphomas, breast tumors, bronchogenic carcinomas, tumors of the testis, and Burkitt's lymphoma. They may be administered with other drugs such as chlorambucil. When administered locally to treat a regionalized neoplasm, counteragents such as folinic acid may be given systemically to counteract the systemic activity of the 8,10-dideazaminoρterin.

The 8, 10-dideazaminopterins are in the class of antineopiastic agents designated antimetabolites. Like methotrexate, they bind tightly to DHFR and prevent the enzyme from activating the conversion of dihydrofolate to tetrahydrofolate. The blockage of this pathway inhibits DNA synthesis thereby inhibiting reproduction of malignant cells. Accordingly, as used herein the term "therapeutically effective amount" means a quantitiy of one or more of the invention compounds that, when administeed to a patient inhibits neoplastic growth. The compounds of the invention thus function similarly to methotexate in therapy but have enhanced antitumor potency and spectrum of activity as compared to methotrexate.

The following examples are illustrative:

Example 1: Preparation of 10-Methyl-8,10-dideazaminopterin

Step 1. Dimethyl α-Methylhomoterephthalate

A solution of dimethyl homoterephthalate (4.16 g, 20 mmoles) in 15 ml of dry tetrahydrofuran was added dropwise over 15 min to a stirred mixture of potassium hydride (2.5 g of 35% oil suspension, 22 mmole) in 75 ml of dry tetrahydrofuran at 0ºC. After 30 min a homogeneous yellow suspension had formed. Methyl iodide (2.79 g, 22 mmole) was then added over a 5 minute period and the resulting mixture stirred for 30 minutes. The mixture was quenched with 2 ml of 50% acetic acid, diluted with 500 ml of water and extracted with ether. The ether extract was washed with water, dried over magnesium sulfate and evaporated to leave an oil. The material was chromatographed on silica gel with elution by ether-hexane (1:9) to afford (71%) of a clear oil; m/e 222 (M⁺): NMR (CDCI₃) 1.50 (3 H, d, CH₃), 3.65 ( 3H, s, OCH₃ ) , 3.93 (3 H, s, OCH₃ benzoate) .

Step 2. 4-Amino-4-desoxy-10-carbomethoxy-10-methyl- 8,10-dideazapterate (Dimethyl Ester) To a stirred mixture of 5.24 g of 22.3% oil suspension of KH (29.2 mmol) and 24 ml of dry DMF at 0º was slowly added 6.48 g (29.2 mmol) of the dimethyl α-methylhomoterephthalate prepared in Step 1. After 30 min the yellow solution was cooled to -40º and 3.6 g (9.2 mmol) of the bromomethyl deazapterin in 48 ml of DMF was added over a 10 min period. The mixture was brought to ambient temperature and stirred for 2 hr. The solvent was removed in vacuo and the residue was partitioned between 100 ml of CHCI₃ and 25 ml of water. The CHCI₃ solution was dried (MgSO₄), concentrated in vacuo and chromatographed on silica gel with initial elution by CHCI₃ to remove unreacted ester, followed by elution of product by CH₃OH/CHCI₃ (1:6) to afford 2.85 g (78%) of a yellow solid 4-amino-4-desoxy-10-methyl-10-carbomethoxy-8,10-dideazapteroate, m/e 395 (M⁺); NMR (d₆-DMSO) 1.50 (3H, s, CH₃), 3.53 (1H, d, C-9 H) , 3.59 (3H, s, OCH₃), 3.72 (1H, d, C-9 H), 3.86 (3H, s, benzoate OCH₃), 7.32 (1H, d, C-7 H) , 7.47 (1H, d, C-8 H) , 7.54 (2H, d, 3',5'-H's), 7.96 (2H, d, 2',6'-H's).

Anal. C₂₂H₂₁O₅O₄.H₂O

Calc'd: C, 58.1; H, 5.61; N, 16.9

Found: C, 58.4; H, 5.30; N, 17.0.

Step 3. 4-Amino-4-desoxy-10-methyl-8,10- dideazapteroic Acid The 10-methyldiester from Step 2 (2.85 g, 7.22 mmol) and 1.06 g (21.7 mmol) of NaCN in 50 ml of DMSO were stirred at 175-180° under N₂ for 2.5 hr. The dark mixture was cooled and the solvent removed in vacuo . The residue was dissolved in 45 ml of water, the solution filtered and the filtrate acidified with HOAc. The precipitate was collected, washed with water and dried to leave 2.28 g (96%) of 4-amino-4-desoxy-10-methyl-8,10-dideazapteroic acid; m/e 323 (M⁺); NMR (d₆-DMSO) 1.23 (3H, d, CH₃ ) , 3.06 (2H, m, 9-CH₂), 3.50 (1H, m, 10-H) , 7.27 (1H, d, 7-H) , 7.39 (3H, m, 8-H, 3',5'-H's), 7.82 (2H, d, 2',6'-H's). Step 4. 10-Methyl-8,10-dideazaminoρterin Diethyl Ester A mixture of 2.38 g (7.3 mmol) of the diamino-10-methylρteroic acid prepared in Step 3, 52.03 ml (14.7 mmol) of triethylamine and 54 ml of dry DMF was treated dropwise with 1.9 ml (14.7 mmol) of isobutyl chloroformate. The mixture was stirred at room temperature for 1 hr and a mixture of 3.52 g (14.7 mmol) of diethyl L-glutamate-HCl, 2.03 ml (14.7 mmol) of triethyl amine and 18 ml of DMF was added. The mixture was stirred at ambient temperature for 24 hr and the solvent was removed in vacuo. The residue was partitioned between 50 ml of sat'd. NaHCO₃ and 50 ml of CHCI₃, followed by two additional CHCI₃ extractions. The CHCI₃ extract was dried (MgSO₄) and evaporated. The crude material was chromatographed on 110 g of silica gel with initial elution by CHCI₃, then removal of the product by MeOH/CHCl₃ (2.5:97.5) to give 2.01 g (54%) of 10-methyl-8,10-dideazaminopterin diethyl ester as a yellow gum, m/e 508 (M⁺); NMR (CDCI₃) 1.23 (9H, m, 10-CH₃, COOCH₂CH₃ ) , 2.4 (4H, m, CH₂CH₂COOCH₂CH₃) , 3.1-3.5 (3 H, m, 10-H, 9-CH₂) , 4.3 (4H, q, COOCH₂CH₃ ) , 4.8 (1H, d, CONHCH, 7.2-7.4 (4H, m, 3'-H, 5'H, 7-H, 8-H) 7.8 (2H, d, 2'-H, 6'-H).

Step 5. 10-Methyl-8,10-dideazaminopterin

A solution of 0.43 g of the 10-methyl-8,10- dideazaminopterin diethyl ester prepared in Step 4 in 6.5 ml of 2-methoxyethanol was treated with 4.3 ml of IN NaOH. The solution was maintained at ambient temperature for 3 hr and diluted with 35 ml of H₂O. The solution was acidified with HOAc to precipitate the product. After refrigeration for 24 hr the precipi tate was collected, washed with H₂O and dried to leave 0.265 g (70%) of 10-methyl-8,10-dideazaminopterin also as a pale yellow microcrystalline solid; m/e as tetratrimethylsilyl derivative, 740, (M⁺) .

Example 2: Preparation of 10-ethyl-8,10-dideazaminopterin

Step 1. Dimethyl g-ethyl Homoterephthalate

Using the procedure of Step 1, Example 1, but substituting for methyl iodide, ethyl iodide, dimethyl α-ethyl homoterephthalate was obtained in 72% yield, m/e 236; NMR (CDC1₃) 0.9 (3H, t, CH₃), 2.0 (2H, m, CH₂CH₃), 3.5 (1H, m, CHC₂H₅) 3.70 (3H, s, OCH₃ ) , 3.90 (3H, s, benzoate OCH₃)

Step 2. 4-Amino-4-desoxy-l0-carbomethoxy-10-ethyl- 8,10-dideazapteroic Acid Dimethyl Ester

Using the procedure of Step 2 of Example 1, and the product of Step 1 of this Example, 4-amino-4-desoxy-10-carbomethoxy-10-ethyl-8,10-dideazapteroic acid dimethyl ester was obtained in 74% yield, m/e 409 (M⁺); NMR (d₆-DMSO) 0.73 (3H, t, CH₃ ) , 2.20 (2H, m, CH₂CH₃ ) , 3.67 (5H, m, 9-CH₂, COOCH₃ ) , 3.90 (3H, s, benzoate OCH₃).

Step 3. 4-Amino-4-desoxy-10-ethyl-8,10- dideazaminopteric Acid Using the procedure of Step 3 of Example 1, and the product of Step 2 of this Example, 4-amino-4-desoxy-10-ethyl-8,10-dideazaminopteric acid was obtained and analytical samples obtained by recrystallization from DMSO. Calcd for C₁₈H₁₉N₅O₂. C, 64.1; H, 5.68; N; 20.8; Found: C, 63.9; H, 5.78; N, 20.5;

UV abs: 238 nm, ε = 35,374; 343 nm, ε = 5,134.

Step 4. 10-Ethyl-8,10-dideazaminopterin Diethyl Ester Using the procedure of Step 4, Example 1, and the product of Step 3 of this Example, 10-ethyl- 8,10-dideazaminoρterin diethyl ester was obtained in 34% yield, m/e 522 (M⁺) .

Step 5. 10-Ethyl-8,10-dideazaminopterin

The 10-ethyl-8,10-dideazaminopterin diethyl ester of the previous step was hydrolyzed under the conditions of Step 5, Example 1 to give 10-ethyl-8,10-dideazaminopterin as C₂₃H₂₆N₆O₅.1.25 H₂O. Calcd: C, 56.5; H, 5.87; N, 17.2; Found: C, 56.6; H, 5.91, N, 17.0; UV absorption max: 238 nm, ε = 37,652; 343 nm, ε = 5,298.

Example 3: Preparation of 10-Propyl-8,10- dideazaminopterin

Step 1. Dimethyl α-Propylhomoterephthalate

Dimethyl homoterephthalate was alkylated as in Example 1, Step 1 but with propyl bromide to afford the α-propyl product in 74% yield as an oil, m/e 250 (M⁺); NMR (CDCl₃) 0.91 (3 H, t, CH₃ ) , 1.26 (2 H, m, -CH₂CH₃ ) , 1.75-2.05 (2 H, m, -CH₂C₂H₅) , 3.62 (1 H, t, -CH-C₃H₇), 3.66 (3 H, s, OHC₃ ) 3.91 (3 H, s, benzoate OCH₃ ) . Step 2. 4-Amino-4-desoxy-10-carbomethoxy-10-propyl- 8,10-dideazapteroic Acid Dimethyl Ester The procedure described in Example 1, Step 2 was carried out except that dimethyl α-propylhomoterephthalate was reacted with the bromomethyl compound. The product diester was obtained as a yellow solid in 45% yield; m/e 423 (M⁺); NMR (d₆-DMSO) 0.72 (3 H, t, CH₃), 1.05 (2 H, m, -CH₂CH₃ ) , 1.92 (2 H, m, -CH₂C-COOMe) 3.57 (3 H, s, COOCH₃ ) , 3.63 (2 H, m, 9-H's), 3.85 (3 H, s, benzoate COOCH₃) .

Step 3. 4-Amino-4-desoxy-10-propyl-8,10- dideazaminopteroic Acid The diemthyl ester of Step 2, this Example, was decarboxylated as in Example 1, Step 3, to give the 10-propyl product as a yellow solid in 81% yield, m/e 351 (M⁺); NMR (d⁶-DMSO) 0.82 (3 H, t, CH₃ ) , 1.15 (2 H, m, CH₂ , CH₃), 1.63 (2 H, m, -CH₂CH) , 3.1 (2 H, m, 9-CH₂), 3.5 (1 H, m, 10-H) , 7.20 (1 H, d, 7-H) , 7.31 (1 H, d, 8-H), 7.36 (2 H, d, 3',5'-H's), 7.79 (2 H, d, 2' ,6'-H's).

Steps 4 and 5. 10-Propyl-8,10-dideazaminopterin

The pteroic acid was condensed with diethyl L-glutamate in the manner described in Example 1, Step 4. The crude ester was obtained in 38% yield; TLC (CHCl₃-MeOH, 9:1) R_f 0.40; m/e 536 (M⁺) . The ester was saponified as in Example 1, Step 5, to give the product 10-propyl-8,10-dideazaminopterin in 53% yield, m/e for the tetratrimethylsilyl derivative, 768 (M⁺). Example 4: Preparation of 10-Amyl-8,10- dideazaminopterin

Step 1. Dimethyl α-Amylhomoterephthalate

Dimethyl homoterephthalate was alkylated as in Example 1, Step 1, but with n-amyl bromide to give the α-amyl product in 72% yield as an oil after chromatography on silica gel; m/e 278 (M⁺); NMR (CDCl₃) 0.84 (3 H, t, CH₃), 1.25 (6 H, m, -CH₂CH₂CH₂-) , 1.77-2.07 (2 H, m, -CHCH₂-) , 3.60 (1 H, t, -CH- C₅H₁₁), 3.66 (3 H, s, OCH₃), 3.91 (3 H, s, benzoate OCH₃ ) .

Step 2. 4-Amino-4-desoxy-10-carbomethoxy-10-amyl- 8,10-dideazapteroic Acid Dimethyl Ester The procedure described in Example 1, Step 2, was carried out except that dimethyl α-amylhomoterephthalate was reacted with the bromomethyl compound. The product was obtained as a yellow solid in 29% yield, m/e 451 (M⁺); NMR (d⁶-DMSO) 0.71 (3 H, t, CH₃), 0.95-1.30 (6 H, m, -CH₂CH₂CH₂-) , 1.92 (2 H, m, -CH2-C-COOCH₃) 3.57 (3 H, s, COOCH₃), 3.63 (2 H, m, 9-H's), 3.85 (3 H, s, benzoate COOCH₃ ) .

Step 3. 4-Amino-4-desoxy-10-amyl-8,10-dideazapteroic Acid The dimethyl ester was decarboxylated as in Example 1, Step 3 to give the 10-amyl product as a yellow solid in 58% yield; m/e 379 (M⁺) .

Steps 4 and 5. 10-Amyl-8,10-dideazaminopterin

The pteroic acid from Step 3 was coupled with diethyl L-glutamate in the manner described in Example 1. The crude ester was obtained and was chromatographed on silica gel with elution by chloroform-methanol, 19:1; m/e 564 (M⁺) . The purified ester was saponified as in Example 1, to give the product 10-amyl-8,10-dideazaminopterin in 60% yield; m/e for the tetratrimethylsilyl derivative 796 (M⁺) .

Exaπtple 5 :

The effectiveness of the invention compounds as antineopiastic agents may be demonstrated by subjecting them to the L-1210 murine leukemia assay. This is a standard assay that is used to evaluate the efficacy of compounds as antineopiastic agents for treating humans. The assay is described by D.J. Hutchinson, D.C. Robinson, D. Martin, O.L. Ittenson and Dillenberg, Journal Cancer Research, (1962) 22:57- 72. It is a procedure for evaluating a compound for increase in median life span in treated animals and untreated controls both infected with L-1210 leukemia cells. The test hydroxide, adjusted to pH 7, and the solution diluted to 10 ml with distilled water. Mice are injected once per day every other day for a total of 5 injections starting one day after transplantation of 10⁶ tumor cells/mouse. The results of this assay with several 8,10-dideazaminopterin analogs were as follows:

Cells

Compound Dose:Mg/Kg ILS% Remaining

8,10-dideazaminqpterin 0.75 +189 4000 10-methyl-8,10-dideazaminopterin 0.6 +203 1000 10-ethyl-8,10-dideazaminqpterin 1 .5 +235 100 10-n-propyl-8,10-dideazaminopterin 6.0 +176 10 ,000

MTX 15 +187

Control - -

It is apparent from the above results that the life spans of the mice were increased considerably by administration of the invention compounds, and that these compounds have surprising activity when compared to the non-alkylated and n-propyl analogs. The % ILS data represent comparisons of log values, and thus differences in the % ILS which appear minor mask large differences in cytotoxic activity. Thus, as shown, the ethyl derivative is 40 times as effective as the unsubstituted compound and 100 times as effective as the n-propyl derivative in terms of reducing the number of neoplastic cells; ie, eg, the number of cells remaining after 10-ethyl analog treatment is only 1/40 and 1/100 of that remaining from treatment with the above analogs, respectively. The assay and these conclusions are described by Schabel, F.M., Symposium on Proliferation and Spread of Neoplastic Cells , M.D. Anderson, Tumor Institute, Houston, Texas (1968) p. 379 ff.

Modifications of the above described modes for carrying out the invention that are obvious to those of skill in organic chemistry synthesis, pharmaceutical formulation, cancer therapy, and/or related fields are intended to be within the scope of the following claims.

Claims

1. A compound of the formula

where R is methyl or ethyl and pharmaceutically acceptable salts thereof.

2. The compound of claims 1 wherein said pharmaceutically acceptable salts are sodium salts.

3. 10-Methyl-8,10-dideazaminopterin.

4. 10-Ethyl-8,10-dideazaminopterin.

5. An antineopiastic composition comprising a therapeutically effective amount of the compound of claim 1 or a salt thereof combined with a pharmaceutically acceptable carrier.

6. A method of inhibiting neoplastic growth in a living animal comprising administering a therapeutically effective amount of the compound of claim 1 or a salt thereof to the animal.